Devices and systems using acoustic energy, particularly within the ultrasonic range (acoustic waves with a frequency greater than about twenty kilohertz (20 kHz), and more typically between fifty kilohertz and five Megahertz (0.05-5 MHz)), have been used to diagnose and treat patients. For example, ultrasonic energy may be employed to obtain images of a region of a patient during a diagnostic or therapeutic procedure. In addition, ultrasound systems have been used for treating tissue, e.g., by focusing acoustic energy towards a target tissue region within a patient, such as a cancerous or benign tumor, to necrose or otherwise heat the tissue region. For example, one or more piezoelectric transducers may be disposed adjacent a patient's body and used to deliver high intensity acoustic waves, such as ultrasonic waves, to an internal tissue region of a patient to treat the tissue region. An exemplary focused ultrasound (“FUS”) system is disclosed in U.S. Pat. No. 4,865,042 issued to Umemura et al.
Focused ultrasound procedures may allow a patient to be treated without requiring invasive surgery. Because ultrasonic transducers are generally disposed adjacent to the patient, however, the acoustic path to a target tissue region may be at least partially obstructed, e.g., by anatomical objects such as bones or cavities, within the patient's body. Furthermore, acoustic energy may not be adequately focused at a location deep within a body, e.g., because the resulting focal zone may be too large to provide an effective and safe treatment. As such, it is preferable to place the transducer as close to a target site as possible.
To deliver acoustic energy to locations deep within the body, it has been suggested to use natural body passages to place an acoustic transducer closer to a target site. For example, U.S. Pat. No. 5,666,954 discloses a transducer that may be inserted into the rectal canal through the rectal orifice to treat prostate cancer. Natural body passages, however, may limit the size of the transducer that may be introduced.
Generally, a relatively large transducer provides better control over the size and intensity of the resulting focal zone. The size of a transducer that may be delivered inside a body passage may be limited by the size of a body orifice at the entry point for the transducer. For example, the size of a transducer used for treating prostate cancer may be limited by the maximum perimeter of the rectal orifice.
Accordingly, apparatus and methods for delivering acoustic energy within a patient's body would be useful.